Electric high-pressure discharge tube



W. ELENBAAS ELECTRIC HIGH-PRESSURE DISCHARGE TUBE Nov. 22, 1949 FiledMarch 30, 1945 INVENTOR: WLLEM EILENBAA IS ATTORNEY Patented Nov. 22,1949 Willem Elenbaas, Eindhoven, Netherlands, assignor to GeneralElectric Company, Schenectady, N. Y.

\ Application March 30, 1946, Serial No. 658,409

In the Netherlands August 13, 1942 Section 1, Public Law 690, August a,194i; Patent expires August 13, 1962 My invention relates to electrodestructures,

and more particularly to electrode structures for high pressure electricdischarge devices such as high pressure electric lamps.

It is common to equip high-pressure discharge tubes (i. e. dischargetubes wherein the pressure during normal operation has such a value thatthe discharge is contracted) with incandescent electrodes consisting ofa core coated with a layer of a substance having a highelectron-emitting capacity, which layer often entirely or partlyconsists of alkaline earth oxides. These incandescent electrodes areusually not heated by a separate heating current, but exclusively by thedischarge so that only one supply conductor is required for eachelectrode. In many cases such an electrode is nevertheless provided withtwo supply conductors, of which only one is used during operation orwhich are electrically interconnected.

The core of this incandescent electrode consists of metal (as a rule ofa refractory metal such as tungsten) and is frequently helically wound.Furthermore, it is known to wind a second wire helically on a metalwire, the assembly being helically wound again. In this way a solidassembly can be obtained which is adapted to be secured only by one endto a supporting wire, the axis of the helix coinciding with the axis ofthe discharge tube. After that the cores thus formed,

as has already been stated above, are coated with a layer having a lowwork function (less than three volts).

The invention concerns high-pressure discharge tubes having one or moreincandescent electrodes that are heated solely by the discharge duringnormal operation and consist of a metal core coated with a substancehaving a high electronic emitting capacity. The invention purports toimprove these discharge tubes, more particularly as regards theincandescent electrodes available therein.

According to the invention the core of these electrodes is shaped as aband and is so folded as to form a reentrant part containing thesubstance having a higher electron-emissive capacity.

In order to be able to emit a suflicient quantity of electrons theemitting substance of an incandescent electrode, which is not separatelyheated, must be heated to the required temperature by the dischargewhich in high-pressure discharge tubes acts only at a comparativelysmall part of the cathode. This is accompanied 6Claims. (c1. 176 -126) 2before the incandescent electrode. evolved where the discharge acts israpidly carried away from this point this involves a higher cathode dropwhich means not only an increase in loss of energy but also a strongdisintegration of the electrode.

When the core of the incandescent electrode I in the discharge accordingto the invention is shaped as a band the dissipation of heat throughthis core can be made very low. In fact, it has 10 times the thickness.Since the band-shaped core, to which as such the emitting substancecannot easily be secured in a sufficiently rigid manner, is providedwith a reentrant part a more or less pocket-shaped part is formed inwhich the emitting substance can be easily introduced in a sufiicientquantity.

Moreover, the electrode has a low weight so that the risk of breaking ofthe electrode from the supporting wire to which it is attached, whichsometimes occurs in transporting the discharge tube, is but small. Inaddition the cost of manufacture is low.

The invention will be more fully explained by reference to the drawingrepresenting, by way of example, one embodiment thereof.

In Fig. 1 the reference number I designates a high-pressuremercury-vapour discharge .tube made from hard glass or quartz.

Each end of the tube contains an electrode 2 which is represented inperspective in Fig. 2. The

core of this electrode consists of a strip of tungsten having athickness of 0.1 mm., a width of 5 mms. and a length of 20 mms. Thisstrip is folded in the form of a heart having a reentrant part 3containing the electron-emissive substance 4 consisting, for instance,of alkaline earth oxide (more particularly barium and/or strontiumoxide) mixed, if required, with other substances such as, for instance,strontium oxide and quartz powder. Both ends of the tungsten strip,which with its flat side is positioned perpendicularly to the axis ofthe tube, are secured to a lead-in conductor or wire 5-which is sealedinto the wall of the tube with the interposition of a bead 6. The

folded strip of electrode 2 in the embodiment by a certain cathodedrop 1. e. a voltage'loss Just as shown in Figs. 1 and 2 is providedwith a re-entrant part forming a substantially cylindrical- If the heat3 shaped groove which is transverse to the axis of the arc dischargepath.

The discharge tube is filled with a rare gas, for instance, argon, at apressure of 4 mms. and furthermore contains a quantity of mercury whichis small so that the mercury vapour, after the tube has attained itsstate of equilibrium, is unsaturated. In this rare gas mercury-vapouratmosphere 9. high-pressure discharge takes place, the vapour pressuremounting to about 1 atmosphere. The tube which may be used for theemission of visible light or ultraviolet rays and has an internaldiameter of 25 mms. and a distance between the electrodes of 100 ms. isfed from an alternating current supply and operated with a currentstrength of 2.5 amps, the voltage difference between the electrodes thenbeing 120 volts.

The shape of the electrodes may be different from that represented inFig. 2. Fig. 3, for instance, represents another shape which is alsovery practicable.

The electrodes used in the tube have a low weight and can be easilyshaped, whereby the manufacture of the electrodes and consequently ofthe tube is rendered cheap. The dissipation of heat from the point wherethe discharge acts is very low owing to the tungsten strip.

What I claim is:

1. In a high pressure arc discharge device comprising spaced electrodestructures for sustaining an arc therebetween, at least one of saidelectrode structures comprising a lead-in conductor and a folded stripof thin refractory metal sup ported by said conductor and having are-entrant part forming a groove extending laterally across the stripand facing the arc path and transverse thereto, and electron-emissivematerial in said groove.

2. In a high pressure are discharge device comprising spaced electrodestructures for sustaining an arc therebetween, at least one of saidelectrode structures comprising a lead-in conductor and a folded stripof thin tungsten supported by said conductor and having a re-entrantpart forming a groove extending laterally across the strip and facingthe arc path and transverse thereto, and an electron-emissive materialcomprising an alkaline earth oxide in said groove.

3. In a. high pressure are discharge device comprising spaced electrodestructures for sustaining an arc therebetween, at least one of saidelectrode structures comprising a lead-in conductor and a folded stripof refractory metal havlog a thickness of 0.1 mm. supported by saidconductor and having a re-entrant part forming a groove extendinglaterally across the strip and facing the arc path and transversethereto, and electron-emissive material including an alkaline earthoxide in said groove.

4. In a high pressure are discharge device comprising spaced electrodecombinations for sustaining an arc therebetween, at least one of theelectrode combinations comprising a lead-in conductor, a folded strip ofrefractory metal having a re-entrant part forming a groove extendinglaterally across the strip and facing the arc path and transversethereto, the thickness of said strip in microns being less than 100times the discharge device operating ,current in amperes and the widthof said strip being at least 10 times the thickness thereof, andelectron-emissive material in said groove.

5. In a high pressure are discharge device comprising spaced electrodestructures for sustaining an arc therebetween, at least one of saidelectrode structures comprising a lead-in conductor and a folded stripof thin refractory metal supported by said conductor and having are-entrant part forming a substantially cylindrical-shaped recessextending laterally across the strip and transverse to the arc path, andelectron-emissive material in said recess.

6. In a high pressure arc discharge device comprising spaccd electrodestructures for sustaining an arc therebetween, at least one of saidelece trode structures comprising a lead-in conductor and a folded stripof thin refractory metal secured at bothends to said conductor andhaving intermediate its ends a reentrant part forming a groove extendinglaterally across the strip and facing the arc path and transversethereto, and electron emissive material in said groove.

WILLEM EIENBAAS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

